rocqPackages.mkRocqDerivation: change prefix for coq

Make the default prefix be set to `[ "coq" ]` if `useCoq` is `true`.

This ensures that `mkRocqDerivation` can be called directly to build
Coq derivations without changing the derivation name / `opam-name`.

pkgs/build-support/rocq/default.nix

@@ -55,7 +55,7 @@ in
   extraNativeBuildInputs ? [ ],
   overrideBuildInputs ? [ ],
   overrideNativeBuildInputs ? [ ],
-  namePrefix ? [ "rocq-core" ],
+  namePrefix ? null,
   enableParallelBuilding ? true,
   extraInstallFlags ? [ ],
   setROCQBIN ? true,
@@ -66,7 +66,7 @@ in
   dropDerivationAttrs ? [ ],
   useDuneifVersion ? (x: false),
   useDune ? false,
-  opam-name ? (concatStringsSep "-" (namePrefix ++ [ pname ])),
+  opam-name ? null,
   useCoq ? false,
   useCoqifVersion ? (x: false),
   ...
@@ -160,10 +160,12 @@ let
       ] ""
     )
     + optionalString (v == null) "-broken";
-  append-version = p: n: p + display-pkg n "" rocqPackages.${n}.version + "-";
-  prefix-name = foldl append-version "" namePrefix;
   useDune = args.useDune or (useDuneifVersion fetched.version);
   useCoq = args.useCoq or (useCoqifVersion fetched.version);
+  namePrefix = args.namePrefix or [ (if useCoq then "coq" else "rocq-core") ];
+  append-version = p: n: p + display-pkg n "" rocqPackages.${n}.version + "-";
+  prefix-name = foldl append-version "" namePrefix;
+  opam-name = args.opam-name or (concatStringsSep "-" (namePrefix ++ [ pname ]));
   rocq-core = if useCoq then coq // { rocq-version = coq.coq-version; } else args0.rocq-core;
   rocqlib-flags = [
     "COQLIBINSTALL=$(out)/lib/coq/${rocq-core.rocq-version}/user-contrib"